The present invention relates to failure detection circuits for stepping motors having a rotor which is driven stepwisely in response to successive energization of its stator coils, and in particular to a circuit for detecting a failure in switching circuits associated with the coils and an open circuit in the coils prior to the time the rotor is set in motion.
The stepping motor comprises a plurality of stator coils which are successively energized in response to pulses applied to the bases of transistors connected in series with the stator coils respectively. To ensure that the rotor be set in motion from a predetermined angular position, a particular set of stator coils is energized to maintain the rotor in that angular position preparatory to the starting of the motor when power is switched in.
A failure detection circuit known in the art permits detection of an open circuit failure of the transistors associated with the initially energized stator coils and detection of an open circuit in the initially not energized stator coils and a short circuit failure of the transistors associated with the latter stator coils. However, other failures including open circuit of the initially energized stator coils, short circuit of the transistors associated with the initially energized coils and an open circuit failure of the transistors associated with the initially not energized coils, are not detected until the rotor has been set in rotation.
The inability of the prior art detection circuit to ascertain all possible failures of a stepping motor prior to its operation is disadvantageous since it results in delay in taking necessary actions to remove the failed components with a resultant loss of its operating time.